Method for operating an otto-cycle internal combustion engine with fuel injection on a cold start

ABSTRACT

A method is provided for operating a spark ignition internal combustion engine having fuel injection at a cold start. The method retards the spark angle to a cold start value at least for the first combustion in at least one cylinder of the internal combustion engine during a cold start phase, the fuel injected into the cylinder being brought to combustion, and the method sets the spark angle to normal, to end the cold start phase.

[0001] The present invention relates to a method of operating a sparkignition internal combustion engine having fuel injection at a coldstart according to the preamble of claim 1.

BACKGROUND INFORMATION

[0002] To start a spark ignition internal combustion engine havingdirect fuel injection, an initial pressure of around 4 bar, for exampleis, built up using an electrical fuel pump. The fuel injection itself islimited by an angle window whose beginning is normally defined by themoment of opening of an inlet valve and whose end is determined by thecombustion chamber pressure that becomes established in the cylinder.Since the pressure in the combustion chamber rises during a compressionphase and, starting at a certain piston position, exceeds the initialpressure built up by the electrical fuel pump, the fuel injection mustbe ended when the pressure in the combustion chamber exceeds a certainpressure threshold. Otherwise, air would incorrectly be blown from thecombustion chamber into the inlet valve, so that instead of fuel thisair would be injected through the inlet valve into the combustionchamber during the subsequent injection. This would disadvantageouslycause combustion misfiring in the corresponding cylinders.

[0003] Consequently the beginning and the end of a fuel injectionlimited by an angle window are determined by a certain rotational angleposition of the crankshaft, the respective rotational angle positions atthe beginning and end of the injection enclosing a correspondingvariable angle of rotation of the crankshaft. The time interval duringwhich the crankshaft passes through this angle of rotation isproportional to the rotational speed of the engine.

[0004] When the internal combustion engine is cold-started, very longinjection times are needed at least for the first combustions. When thefuel injection times are very long, the fuel which reaches thecombustion chamber from the first two injections comes to combustion andcauses a significant increase in rotational speed. Because of therelatively great increase in rotational speed, there is no longersufficient injection time available for the subsequent third and fourthinjections to be able to inject an adequate quantity of fuel forcombustion into the combustion chamber using the inlet valve (injectionvalve). This causes unwanted combustion misfirings at the third andfourth injections during the cold start.

[0005] To avoid these unwanted combustion misfirings during the coldstart, it is known that an additional injector (cold start injector) maybe provided, which is positioned in the intake pipe of the engine andinjects additional fuel into the injection chamber simultaneously withthe intake valve during the cold start. Providing such an additionalcold start valve is relatively complicated and costly.

ADVANTAGES OF THE INVENTION

[0006] The method according to the present invention for operating aspark ignition internal combustion engine having fuel injection at acold start is characterized by the following procedural steps:

[0007] retarding the spark angle to a cold start value for at least thefirst combustion in at least one cylinder of the internal combustionengine during a cold start phase, while the fuel injected into thecylinder is brought to combustion;

[0008] setting the spark angle to normal to end the cold start phase.

[0009] Since the spark angle is retarded as far as possible for at leastthe first combustion in at least one cylinder, the fuel or fuel-airmixture injected into the combustion chamber is burned up in thecorresponding ignition, and advantageously a very small torque isproduced by this combustion.

[0010] Consequently, the first combustion using retarded spark angleresults in a very slight increase in rotational speed, so that there isalso sufficient injection time available for the next immediatelyfollowing injection to be able to inject sufficient fuel into thecombustion chamber to ensure reliable combustion. At the same time itmust also be kept in mind that already after the first combustion thecombustion chamber is warmed up sufficiently so that significantly lessfuel needs to be injected into the combustion chamber to ensure a nextcombustion. Thus a retarding of the spark angle for at least the firstcombustion in each respective cylinder during a cold start results inwarming of the combustion chamber while the increase in rotational speedof the engine is sharply reduced. In this way successful combustion isensured for the next injection, since less injected fuel is needed forthe following combustion because of the warming of the combustionchamber by the first combustion, while at the same time more injectiontime is available for injecting fuel into the (warmed) combustionchamber due to the relatively slight increase in rotational speed. Thuscombustion misfirings during cold starting are prevented or reduced in asimple and reliable way.

[0011] Preferably the cold start phase includes a plurality ofcombustions. Because of the very low increase in rotational speed duringthe first combustions with very late spark angle, the retardation of thespark angle is not limited to the first combustion during the coldstart, but can be extended to a desired optimal number of combustions toachieve effective warming of the combustion chamber and to optimizeadditional cold start parameters.

[0012] With advantage the spark angle is reset to normal in a singlestep to set a desired operating performance value. This makes itpossible after the cold start phase ends to change quickly from retardedspark angles to appropriate normal spark angles, at which elevated ormaximum possible spark angle operating efficiency can be achieved.

[0013] Advantageously the spark angle is reset to normal in a pluralityof transitional steps to set a desired operating performance value. Toavoid too great a change in the spark angle, the reset to normal inorder to end the cold start phase can also take place in severaltransitional steps, until the desired normal spark angle is set in orderto utilize maximum possible spark angle operating efficiency.

[0014] According to a preferred embodiment version, the cold start valueis set individually for each cylinder. Since the cold starting responseof the various cylinders of an internal combustion engine may bedifferent, it is advantageous to calculate and set a necessary coldstart value for each individual cylinder, in order to ensure effectiveprevention of combustion misfirings while at the same time maintainingthe maximum possible spark angle efficiency.

[0015] Preferably the cold start value is set during the cold startphase for the next combustion of each corresponding cylinder. Sinceincreased warming of the combustion chamber is achieved during the coldstart phase with each combustion, it is advantageous to calculate andset a specific cold start value for each individual cylinder for eachindividual combustion. In this way the retardation of the spark angleduring the cold start phase is kept as small as possible, so thatoptimized spark angle operating efficiency can advantageously beattained even during the cold start phase.

[0016] With advantage the cold start value is set using a retardationsetting which is adapted to the operating temperature of the particularcylinder. In this way the cold start value of the spark angle can bekept at the lowest level possible, in order to achieve optimal sparkangle operating efficiency while reliably preventing combustionmisfirings during the cold start phase.

[0017] Advantageously, the spark angle is retarded on condition that thenumber of ignitions is smaller than or equal to the value of a parameterwhich by definition is greater than or equal to one and smaller than orequal to the number of cylinders in the engine, and that at the sametime the combustion chamber temperature before the first ignition islower than a threshold temperature. This makes it possible to limit theretardation during the cold start phase to a defined number ofignitions, for example in the form of alternative polling. At the sametime the combustion chamber temperature before the first ignition can bedetermined at least approximately from the coolant temperature, the oiltemperature and/or the intake air temperature of the engine. Thetemperature threshold can be approximately 0° C., for example.

[0018] Additional advantageous configurations of the present inventioncan be found in the description.

DRAWINGS

[0019] The present invention is explained in greater detail below in oneembodiment on the basis of a corresponding drawing. FIG. 1, the soleFIGURE, shows a block diagram of a cold start spark angle adjustment.

DESCRIPTION OF THE INVENTION

[0020]FIG. 1 shows a block diagram of a cold start spark angleadjustment, where the following definitions apply:

[0021] Block 10=start of the cold start spark angle adjustment;

[0022] Block 11=parameter acquisition with the parameters

[0023] n=freely applicable number where 1≦n≦number of cylinders,

[0024] z=number of ignitions;

[0025] Block 12=alternative polling;

[0026] Block 13=spark angle retardation ΔZW⇓;

[0027] Block 14=spark angle normal setting ΔZW↑;

[0028] Block 15=end of the cold start spark angle adjustment.

[0029] When the internal combustion engine is started (Block 10), thecold start spark angle adjustment is started automatically; the freelyapplicable number designated as n (for example 1≦n≦number of cylindersin the engine) and the number of ignitions designated as z are definedas parameters (Block 11). These parameters n and z are determined bysuitable means. Before the first ignition, z has the value 0. When theengine is cold started, an automatic alternative polling (Block 12)takes place to determine whether the number of ignitions z is smallerthan or equal to the number of cylinders n in the engine (z≦n ?), andwhether at the same time the combustion chamber temperature To in thecylinder before the first ignition is lower than a temperature thresholdTs (To<Ts ?). If this is the case, that is, if both conditions arefulfilled at the same time and the alternative polling is answered withyes, spark angle retardation (Block 13) is activated for the nextignition z+1. The alternative polling (12) is continued until the numberof ignitions z is greater than the number of the parameter n. Startingfrom this moment in the operation, the alternative polling (Block 12) isthus answered with no, so that the spark angle retardation which wasactivated up to this point (Block 13 with z≦n) is canceled by anappropriate advancement of the spark angle (Block 14). After thissetting of the spark angle to normal (Block 14), the cold start angleadjustment is ended (Block 15).

[0030] In this embodiment according to FIG. 1, the retardation of thespark angle is set to a cold start value for a number of ignitions z,which corresponds to the number of the parameter n. This spark angleretardation guarantees that throughout the entire cold start phase thefuel or fuel-air mixture injected into the cylinder each time is broughtto combustion. Since the spark angle is retarded for thefirst-combustions, almost no torque is produced during the cold start,so that the increase in rotational speed is advantageously very slight.As a result there is a relatively long time available for all injectionsduring the cold start phase, and especially for the second through thelast injections (z>1 to z=n), to enable a sufficient quantity of fuel orfuel-air mixture for successful combustion to be injected into therespective cylinder. Thus by retarding the spark angle, disadvantageouscombustion misfirings during the cold start phase can be reliablyprevented or reduced.

[0031] Furthermore, the first combustions in the respective cylinderproduce an advantageous warming of the combustion chamber, for whichreason the fuel or fuel-air mixture which is required to be injectedinto the respective cylinder to guarantee reliable combustion is reducedcompared to a colder combustion chamber for the next ignition. Thismeans that the spark angle requires less retardation with increasingwarming of the combustion chamber, due to the first combustions during acold start phase, in order to guarantee at the same time successfulcombustion of the injected fuel or fuel-air mixture throughout theentire cold start phase. In this way the spark angle operatingefficiency can be optimized during the cold start phase of an internalcombustion engine, since for each ignition in the cold start phase thespark angle is retarded only as much as necessary for successfulcombustion at the time of all ignitions and thus to prevent combustionmisses.

[0032] After a certain, individually adjustable number of ignitions zthe spark angle is set to normal, in order to limit the cold start phaseto as few ignitions as possible and thus to operate the internalcombustion engine at high spark angle operating efficiency with thelargest possible spark angles (advanced ignition point) as quickly aspossible. The spark angle retardation should advantageously cover thefirst ignition during cold starting of a cylinder of the engine, inorder to keep the duration of the start as short as possible. It is alsopossible to provide for a plurality of transitional steps withincreasing spark angle advancement in the transition from the sparkangle retardation to the normal spark angle setting. The optimumretarded spark angle value (cold start value) can be calculated and setindividually for each cylinder of the internal combustion engine.

What is claimed is:
 1. A method of operating a spark ignition internalcombustion engine having fuel injection at a cold start, characterizedby the following procedural steps: retardation (13) of the spark angleto a cold start value at least for the first combustion in at least onecylinder of the internal combustion engine during a cold start phase,the fuel injected into the cylinder being brought to combustion; settingof the spark angle to normal (14) to end the cold start phase.
 2. Themethod according to claim 1, wherein the cold start phase includes aplurality of combustions.
 3. The method according to one of thepreceding claims, wherein the spark angle is set to normal (14) in asingle step to set a desired operating performance value.
 4. The methodaccording to one of the preceding claims, wherein the spark angle is setto normal (14) in a plurality of transitional steps to set a desiredoperating performance value.
 5. The method according to one of thepreceding claims, wherein the cold start value is set for each cylinderindividually.
 6. The method according to one of the preceding claims,wherein the cold start value is set during the cold start phase in eachcase for the next combustion of a respective cylinder.
 7. The methodaccording to one of the preceding claims, wherein the cold start valueis set using a retardation (13) adjusted to the operating temperature ofthe respective cylinder.
 8. The method according to one of the precedingclaims, wherein the retardation (13) takes place on condition that thenumber of ignitions (z) is smaller than or equal to the value of aparameter (n) which by definition is greater than or equal to one andsmaller than or equal to the number of cylinders in the internalcombustion engine, and at the same time the combustion chambertemperature (To) before the first ignition is lower than a thresholdtemperature (Ts).